1. Field of the Invention
The invention relates in general to an overdrive apparatus and associated method applied to a display system, and more particularly to overdrive apparatus and associated method that provides different overdrive tables for different scan lines of an image frame through a simple memory arrangement.
2. Description of the Related Art
A display system, e.g., an LCD display system, is one of the most essential human-machine-interfaces (HMI) in modern electronic systems. It is therefore a research and development target for electronic manufacturers as to how to provide a display system with lower cost and higher performance.
A display system comprises several display units arranged as a plurality of scan lines. When displaying a frame of an image signal, display units on a same scan line respectively correspond to pixels of a same horizontal line in the frame. For example, each display unit displays different color levels of a primary color (e.g., red, green or blue) to indicate a component of the three primary colors.
Based in timing requirements of image display, the display system in sequence updates frames, e.g., updating an f frame to an (f+1) frame. To update a frame, the display system one after another updates the scan lines; that is, the display system updates a first scan line, and a second scan line after having updated the first scan line, and so on. When updating a scan line, a color level C(f), corresponding to one of the display units, of the f frame is updated to a color level C(f+1) of the (f+1) frame according to content of the image data. However, since a response time of the display unit is relatively slower in updating the color levels, it is often that the color level C(f) cannot be updated to C(f+1) in time.
To enhance the response time of the display unit, an overdrive technique is adopted in driving the display system. With overdriving, the display unit is driven to change the color level from C(f) to (C(f+1)+dC) instead of to C(f+1). For example, when the color level C(f+1) is greater than the color level C(f), the color level dC is predetermined to be greater than 0. Therefore, when the display unit is driven to the higher color level (C(f+1)+dC), the desired color level C(f+1) is more quickly achieved. Similarly, when the color level C(f+1) is smaller than the color level C(f), the color level dC is predetermined to be smaller than 0. Therefore, when the display unit is driven to the lower color level (C(f+1)+dC), the desired color level C(f+1) is more quickly achieved. In actual practice, the value of color level dC is obtained from an overdrive look-up table. For example, the overdrive table determines a positive/negative signal and values of the color level dC according to combinations of the color levels C(f) and C(f+1).
In many applications, timing requirements for updating different scan lines may vary. In certain applications, although the display system still updates the scan lines one after another when updating a frame, an updated frame is only displayed to viewers when all scan lines in the frame are updated. For example, in some three-dimensional applications, the display system alternately displays left frames and right frames with a display panel in conjunction with shutter glasses. When the display panel displays the left frames, the glasses open up for the left eye and shield the right eye to present the left frames to the left eye; when the display panel displays the right frames, the glasses at the same time open up for the right eye and shield the left eye to present the right frames to the right eye. Accordingly, the user perceives a three-dimensional image.
However, in the above three-dimensional application, the display system can only present a completely updated frame to the user (with opening and shutting of the glasses) to prevent undesirable effects caused by mixing the left and right frames. That is to say, timing requirements for updating different scan lines are different. When a last scan line of the frame is updated, the entire frame is updated and ready to be presented, and so the last scan line needs a relatively faster response time since it is given a smallest time period from being updated to being presented. In comparison, other scan lines have longer periods from being updated and to being presented and can thus be given with relatively slower response times. For example, a first scan line may have a slowest response time, a second scan line may have a second slowest response time, and so forth. Thus, a last scan line is allowed with a smallest time period and thus needs a fastest response time.
Therefore, to accommodate applications of different response times for different scan lines, the overdrive technique needs to provide different overdrive tables for the different scan lines.